The vertebrate eye and retina have provided important models to identify fundamental processes of developmental such as induction, morphogenesis, patterning and cell fate specification. While a considerate amount of information describing the early events of eye development has been uncovered, many processes of later stages of differentiation and maturation are less well understood. For example, the well characterized, laminar organization of the vertebrate retina is complimented by the non-random or mosaic arrangement of neurons within each of the layers. Though the necessity of the mosaic arrangement is intuitive: gaps in the distribution of neurons or clustering of cells would result in under representation or oversampling of portions of the visual field, little is known of the genetic mechanisms regulating the mosaic patterning. Over the next five years, we propose a novel genetic screen of post-embryonic stage larvae and adult progeny of ENU-mutagenized zebrafish to uncover novel recessive and dominant mutations affecting the visual system. A systematic screen for late onset mutations should provide much needed models of inherited diseases in humans such as retinitis pigmentosa, congenital cataracts and glaucoma. Three specific aims are proposed: SPECIFIC AIM I: Recover novel, recessive mutations that specifically affect the specification and mosaic patterning of photoreceptor cells through an in situ immunohistochemical screen of the rod mosaic in free swimming, 5 day old larvae. SPECIFIC AIM II: Identify genes essential to the development and maintenance of the anterior segment, through a morphological screen for defects in the lens, cornea and pupil of the larval eye. SPECIFIC AIM III: Identify mutations resulting in photoreceptor cell dystrophies as models of human retinal disease through the histological and immunofluorescent analysis of retinas of adult zebrafish. The initial mutagenesis procedure and subsequent breeding strategy incorporated a mapping panel into the mutagenized lines to facilitate more efficient mapping and the subsequent cloning of the mutated genes. Descriptions and images of the mutant phenotypes will be available at the PI's website and the Zebrafish Information Network and distribution will be handled through the Zebrafish International Resource Center.